NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,865 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

A substance that prevents cells from making or using progesterone (a hormone that plays a role in the menstrual cycle and pregnancy). Antiprogestins may stop some cancer cells from growing and they are being studied in the treatment of breast cancer. An antiprogestin is a type of hormone antagonist.